Natural Gas Clothes Dryers (Residential)
Introduction
Most households in Canada dry their laundry in clothes dryers that tumble the clothes in warm air. While hanging clothes on a clothesline outdoors when the weather permits is the most economical and most gentle way of drying, machine drying is more convenient and usually faster, but consumes a considerable amount of energy. All dryers use electricity to power the controls and the motor that drives the drum, but for heating the air that dries the clothes, either electricity or natural gas can be used. There are approximately 9.8 million dryers in use in Canada, 96.9% of which are heated with electricity, and the balance (3.1%) with natural gas. The popularity of gas dryers varies across Canada, since the availability of natural gas and price difference between electricity and natural gas vary considerably from province to province. Ontario and Alberta lead the country in the concentration of gas dryers (with 7.7% and 10.2 % respectively) and Quebec has a very small number, but is growing due to the local utility's efforts to increase availability and market share of natural gas. In the USA, about 20% of the clothes dryers use natural gas; their higher popularity compared to Canada is partly the result of a larger difference between electricity and natural gas prices in the USA.
It is estimated that in Canada, dryers consume a total of 26.4 PJ of energy per year, equivalent to 7.2 billion kWh of electricity.
How do gas dryers work?
Modern natural gas dryers are very similar to electric dryers, except for the way that heat is produced. Both types of dryers draw air from the back of the unit, heat it up either with an electric resistance heating element or with a gas burner, and pass it through the drum where it picks up moisture from the clothes tumbling through the warm air. The humid air is then passed through a lint filter and is finally carried away by a fan that blows it outside through the exhaust duct. A temperature sensor at the dryer exit controls the temperature of the air by cycling the heater or the burner. The drying cycle may be terminated by a temperature sensor at the air exit, by a moisture sensor installed in the drum, or by a timer.
Differences in performance between gas dryers and electric dryers
Gas dryers are available in different capacities, with gas burners ranging in output between 5.3 kW and 8.8 kW (18,000 and 30,000 BTU/h). Electric dryers have heaters ranging up to about 5.6 kW, a limit related to the capacity of the electric supply circuit to the dryer. The higher capacity gas models are faster than electric models, resulting in shorter drying times. Gas dryers produce hot air with more moisture than electric heaters, and are claimed to produce less wrinkling or to de-wrinkle some fabrics more effectively than electric dryers. As far as generation of static electricity is concerned, there appears to be little difference between electric and gas dryers, since it is the friction between fabrics tumbling during the cool-down portion of the cycle that produces static electricity, and this portion of the cycle does not make use of the heat sources.
High end gas dryers have higher gas inputs, operate at higher temperatures, terminate the cooling cycle at a higher temperature and consequently dry faster than regular models. These higher end models are equipped with moisture sensors that prevent over-drying the clothes and thus save energy.
Most manufacturers offer similar conventional (standard or compact) gas dryer models with either natural gas or electricity. Gas-fired dryers cost about $50 more than the equivalent electric model.
Combined washer/dryer appliances
When little space is available for a washer and dryer, there are two options besides the stackable pair, where the dryer can be placed above a front-loading washer (each appliance has its own source of power and individual control system.) These may be standard size or compact size appliances.
- an integrated (standard or compact) washer-dryer, where the individual washer component and dryer component are built on a common frame, with a single source of power and a single set of controls for both functions,
- a combination (standard or compact) clothes washer-dryer, having a single drum for both washing and drying with capacity of less than 45 L (1.6 cubic feet), with a single source of power and single control.
Only conventional individual dryers and integrated washer-dryers may offer natural gas drying as an option. Combination clothes washer-dryers offer only electric drying.
Performance standards for dryers
At the present time, natural gas dryers in Canada are not regulated under the Energy Efficiency Act and Regulations. There is also no ENERGY STAR specification for natural gas or for electric clothes dryers because the difference in performance between models is quite small.
Unlike most other appliances, clothes dryer models do not vary much in the amount of energy that they use for drying an equivalent amount of clothes. While all individual electric dryers are required to meet a specific minimum level of efficiency (measured in terms of weight of clothes dried per unit of energy consumed, kg/kWh), and are also required to have an EnerGuide label, gas dryers do not have these requirements.
Integrated washer-dryer appliances with gas dryers are required to be labeled according to the EnerGuide washer requirements only.
Combination clothes washer-dryers are required to be labeled according to the EnerGuide requirements only for the washing function but are excluded from the minimum efficiency requirement of the drying function.
Venting requirements
All gas dryers must be vented to the outdoors to prevent exposure of the occupants to the products of combustion of the dryer, as well as to prevent the build-up of moisture in the building. Even electric dryers should be vented to the outdoors to prevent the build-up of moisture indoors. The large release of moisture from the dryer, if vented indoors, can cause condensation problems, mold growth on certain surfaces, possible health problems for the occupants and in certain cases, structural damage. In situations where there is no convenient access to the outdoors for venting, a "condensing" or "ventless" electric dryer would be the only alternative. (See "Condensing Dryers"). Although it may be tempting the try and re-use the heat output of electric dryers during the heating season by venting indoors, it is definitely not recommended because it can be harmful to occupants and to the structure. There is no practical way of recovering the heat used by vented dryers to use indoors during the winter. Consumers should ensure that the exhaust from not only natural gas dryers but also from electric dryers is vented safely outdoors.